1. Field of the Invention
The present invention pertains generally to the field of adjustable vehicle seats and more particularly relates to improved mechanisms for adjusting the inclination of the backrest and to an inertia operated lock for a backrest which is normally freely forwardly tiltable.
2. State of the Prior Art
Many reclining mechanisms and a variety of inertia operated locks for vehicle seat backrests are known. Both kinds of devices are extensively used in the automotive field where at least the driver's seat usually has a backrest adjustable to different angles relative to the seat. In the case of two door vehicles having a rear passenger seat, the backrests of the front seats are often provided with hinged mechanisms which in a normal condition allow the backrest to be readily pushed forward and tilted out of the way so as to facilitate access to the back seat. These hinge mechanisms remain unlocked even while the front seat is normally occupied during operation of the vehicle. Such hinges conventionally include inertia operated devices for locking the backrest of the front seats to prevent them from being thrown in the event sudden braking or collision, and to prevent the backrest from falling forward whenever the vehicle is on a steep incline. A variety of mechanisms for accomplishing these objectives are known and in use.
Presently known recliner adjustment mechanisms typically include two members hinged together, a gear rack formed along an arcuate edge of one member and a toothed pawl element pivotably mounted to the other member and movable into engagement with the rack so as to interlock the two members at a selected position. While such mechanisms are generally effective and many variations of the same are known, they suffer from a significant shortcoming in that they require relatively complicated linkages between the pivotable pawl element which is mounted in the vicinity of the hinged joint, i.e. underneath the backrest and towards the rear of the seat, and a release handle which desirably is more accessibly located closer to the front of the seat so as to be within easier reach of the driver. A further shortcoming inherent in pivoting pawl elements is that the teeth on the pawl do not all mesh simultaneously with the teeth on the rack. Due to the pivotal mounting of the pawl, the teeth nearest the pivot point of the pawl mesh with the rack teeth slightly ahead of the pawl teeth distal from the pivot point. It has been found that it is therefore possible for a false engagement to occur between the pawl and the rack in which a single tooth of the pawl engages the rack in such a way as to prevent full meshing of the gear teeth but which upon subsequent application of weight or force to the backrest the pawl disengages from the rack allowing the backrest to fall back to its fully reclined position under the weight of the driver's body, suddenly depriving the driver of back support. Such sudden loss of support in a moving vehicle may be the cause of an accident and such a possibility is clearly undesirable.
Existing inertia locks for vehicle backrests also are deficient in that no mechanism known to this applicant achieves a positive locking action between the backrest and the fixed portion of the seat without allowing some forward tilting of the backrest before the locking action is completed. A further defect in certain existing inertial locking mechanisms is that the mechanism may lock if the backrest is pushed forward too quickly during entry or exit by a passenger. Further, many of the existing inertial locks are unnecessarily complex and simplification of the mechanism is needed.